It is well known that Ca2 ion is required for normal cell growth and is involved in the regulation of a number of cell functions (i.e., cell division, motility, secretion, and maintenance of cell shape). In order to achieve a better understanding of the precise role of Ca2 ion, it is first necessary to determine the specific interaction of Ca2 ion with intracellular components. The specific tasks of this proposal are to study the biochemical mechanisms of Ca2 ion in cells by studying the intracellular Ca2 ion-binding proteins. This will be accomplished by using, in a complementary manner, biochemical and cell morphological techniques. The expected common denominator for mediating Ca2 ion stimulated processes in a ubiquitous low molecular weight protein which binds Ca2 ion with high affinity. Current data suggest that this protein may prove to be the intracellular Ca2 ion-receptor protein. The general approach of this proposal is to study this intracellular Ca2 ion receptor with regard to its biological synthesis, intracellular localization, and involvement in cell division and motility. In particular, the Ca2 ion regulation of microtubules and microfilaments will be investigated. In this manner it is hoped that further insight will be gained regarding the specific mediation of calcium regulated events in the cell.